The present invention relates generally to starting and operating circuits for lighting systems including a high intensity discharge ("HID") lamp and, more particularly, to auxiliary lighting control ("ALC") for such circuits for automatically lighting an auxiliary light source when desired.
Generally, HID lamps will extinguish when power to the lamp is interrupted. Power interruptions of even a very short duration, e.g., tens of milliseconds, will often extinguish the lamp. As is well known, generally, an extinguished HID lamp will not immediately reignite upon the restoration of power to the lamp as cooling of the gases within the lamp is required before the lamp will reignite. Further, when the lamp is reignited, its lumen output is usually only a fraction of normal and gradually increases until the lamp is at full brightness.
Typically, it may take several minutes upon restoration of power to the HID lamp before the lamp is at full brightness. Accordingly, ALC circuitry has been used for automatically lighting an auxiliary light source, such as an incandescent lamp, following a brief power interruption of an HID lamp.
During normal operation of a lighting system comprising an HID lamp and an auxiliary lamp (controlled by the ALC), the HID lamp is ON (energized) and the auxiliary lamp is OFF (deenergized). Typically, the primary winding of a current transformer is series connected with the HID lamp. The ALC senses the ON/OFF condition of the HID lamp by sensing the HID lamp current. The HID lamp current through the primary winding induces a proportional current in the secondary winding of the current transformer.
In prior art ALCs, a relay is maintained in an activated, non-conductive state by the current induced in the secondary winding of the current transformer. The relay operates to isolate power from the auxiliary lamp when in a non-conductive state so that the auxiliary lamp is OFF when HID lamp current is present, i.e., when the HID lamp is ON. When power is interrupted causing the HID lamp to extinguish, the relay is deactivated to a conductive state so that the auxiliary lamp will energize when power is restored to the lighting system.
Thus, typical prior art ALCs operate with a normally closed relay, i.e., a relay which is activated to a non-conductive state to isolate power to the auxiliary lamp and which fails to a conductive state energizing the auxiliary lamp. Faults in such circuits are likely to result in the relay deenergizing to a conductive state or becoming stuck in the conductive state energizing the auxiliary lamp simultaneously with the HID lamp for lengthy periods of time. Such a condition is undesirable because of potential ballast failure in the lamp circuitry.
Further, in such typical prior art circuits, the auxiliary lamp will energize when power is initially applied to the circuit, i.e., a "cold" start of the HID lamp. It is desirable to minimize the time the auxiliary lamp is ON unnecessarily to prolong the life of the lamp and conserve energy.
Many prior art ALCs provide a time delay using a temperature sensitive resistor to keep the auxiliary lamp energized during hot restart of the HID lamp until the HID lamp reaches full brightness. These time delays are susceptible to unpredictable operation due to changes in temperature and duty cycle.
Further, in the prior art ALCs, the current transformer must be sufficiently large so that its output at the secondary winding is sufficient to drive the electromagnetic relay or operate a switch, such as a triac, to apply power to the relay. Such current transformers are costly and bulky. It is desirable therefore, to minimize the size of the current transformer to save costs in the manufacture of such ALCs.
Accordingly, it is an object of the present invention to provide a novel ALC for a HID lighting system and a novel method of controlling an auxiliary light source in a HID lighting system.
It is another object of the present invention to provide a novel ALC and method, providing a normally open electromagnetic relay which fails "safe" to eliminate potential ballast failure caused by simultaneous operation of the HID lamp and the auxiliary lamp.
It is another object of the present invention to provide a novel ALC and method using a solid state control circuit to activate and deactivate the electromagnetic relay.
It is yet another object of the present invention to provide a novel ALC and method in which the auxiliary lamp will not energize during a cold start of the HID lamp.
It is still another object of the present invention to provide a novel ALC and method with reliable and predictable operation which is not influenced by temperature or duty cycle.
It is a further object of the present invention to provide a novel ALC and method which minimizes the size and cost of the current transformer.
It is yet a further object of the present invention to provide a novel ALC and method which protects semiconductor components from power transients.
It is still a further object of the present invention to provide a novel ALC and method which provides a low voltage d.c. power supply to operate components.